Hydrophilic photocatalytic member

The present invention relates to a hydrophilic photocatalyst member that exerts a hydrophilic action, an antibacterial action, and an antifouling action by a photocatalyst.

[0002] Titanium oxide (TiO₂) Is irradiated with ultraviolet rays, titanium oxide (TiO)₂It has been conventionally known that the photocatalytic action of) exerts a hydrophilic action, an antibacterial action and an antifouling action.

[0003] Such titanium oxide (TiO)₂) Is disclosed in JP-A-9-57912, JP-A-10-36144, JP-A-10-57817 and JP-A-10-231146 as prior arts in which) is applied to substrates such as glass and ceramics. There is something. The basic configuration disclosed in these prior arts is that a titanium oxide layer as a photocatalyst is formed on the surface of a glass substrate directly or via an alkali blocking base film, and silicon oxide (SiO) is formed on the surface of the titanium oxide layer.₂) A film is formed.

[0004] The prior art described above is silicon oxide (SiO).₂) The membrane can be made porous or titanium oxide (TiO)₂) By providing fine irregularities on the film and glass substrate, we are devising ways to enhance the photocatalytic action.

[0005] It is known from Wenzel's equation that a hydrophilic surface becomes more and more hydrophilic because the surface area is increased by forming fine irregularities on the surface. However, even if fine irregularities are formed on the surface, the antibacterial action and the antifouling action are not necessarily significantly improved.

[0006] Therefore, titanium oxide (TiO)₂), A proposal focusing on the orientation of the crystal plane is published in Japanese Patent Application Laid-Open No. 10-152396. This prior art is titanium oxide (TiO)₂), The crystal planes selected from (001), (211), (101) and (110) are oriented in the direction perpendicular to the crystal direction, so that the photocatalyst has antibacterial action and antifouling action. It is intended to improve all of the decomposition action and hydrophilic action of organic matter.

[0007] [Problems to be Solved by the Invention] The photocatalytic action is anatase-type titanium oxide (TiO) rather than a rutile-type crystal structure.₂) Is stronger, and therefore it is expected that the photocatalytic action will be affected by the orientation of the crystal plane. However, as described in the prior art described above, some photocatalysts occur when the crystal planes selected from (001), (211), (101) and (110) are oriented perpendicular to the crystal direction. Although improvement in action is observed, it cannot be said to be sufficient.

[Means for Solving the Problems] In order to solve the above problems, the hydrophilic photocatalyst member according to claim 1 has a titanium oxide layer as a photocatalyst directly on the surface of the base material or via a base film for blocking alkali. Is formed, and an overcoat layer is formed on the surface of the titanium oxide layer. The titanium oxide layer has an anatase-type crystal structure, and the crystal planes (101), (112) and (211) is oriented substantially parallel to the surface of the base material. Here, the fact that the crystal planes (101), (112) and (211) are oriented substantially parallel to the surface of the substrate means that the peak due to X-ray diffraction can be captured.

[0009] Further, the hydrophilic photocatalyst member according to claim 2 has a configuration in which the crystal plane (200) is similarly oriented in addition to the above crystal plane.

[0010] In the hydrophilic photocatalyst member according to claim 3, in the hydrophilic photocatalyst member according to claim 1, the crystallite size of the titanium oxide layer is 10 nm or more and 50 nm or less.

[0011] In order to improve the photocatalytic action, the titanium oxide layer preferably has an anatase-type crystal structure, and in particular, the crystal planes (101), (112) and (211) are substantially relative to the surface of the substrate. By being oriented in parallel, the photocatalytic action is fully exhibited. When the thickness of the titanium oxide layer is 200 nm or more, the orientation of the crystal planes (101), (112) and (211) becomes remarkable. Further, it is preferable that the crystal plane (200) is also oriented substantially parallel to the surface of the base material. A more preferable thickness of the titanium oxide layer is 500 nm or more. On the other hand, even if the thickness of the titanium oxide layer is 200 nm or more, the above crystal plane orientation cannot be obtained when the substrate temperature at the time of forming the titanium oxide layer is about 230 ° C or less. This is because when the substrate temperature is set to about 230 ° C or less, the growth of titanium oxide crystals is not sufficient, and the crystallite size becomes less than 10 nm, and as a result, the above crystal plane orientation is not achieved. it is conceivable that.

[0012] Further, in order to improve the hydrophilicity, it is preferable that the surface average roughness (Ra) of the outermost surface of the member is 0.5 to 25 nm. That is, when the surface area is increased by r times by forming fine irregularities on the surface, the contact angle with water when the smooth surface is formed is θ, and the contact angle with water when the irregularities are formed is θ'. Then, from Wenzel's equation, cosθ'= rcosθ (90 °> θ> θ') holds. For example, if unevenness is formed on the surface of a member whose contact angle with water is 30 ° on a smooth surface to increase the surface area by 1.1 times, cosθ'= 1.1cos30 ° = 0.935 from the above equation, and θ'= from this. It becomes 17.7 °. Similarly, when the surface area is multiplied by 1.15, θ'is 5.2 °. When θ is 90 ° or more, that is, when the surface is hydrophobic (water repellent), the larger the surface area, the larger θ'. That is, by forming fine irregularities on the surface, the hydrophilic surface becomes more and more hydrophilic, and the hydrophobic surface becomes more and more hydrophobic.

[0013] In order to make the outermost surface of the member have the above-mentioned surface average roughness, the surface average roughness (Ra) of the titanium oxide layer may be 0.5 to 25 nm. In this case, the unevenness of the titanium oxide layer is transferred to the overcoat layer as it is, and the surface average roughness (Ra) of the outermost surface of the member becomes 0.5 to 25 nm. Whether the surface average roughness (Ra) is smaller than 0.5 nm or larger than 25 nm, the long-term stability of hydrophilicity is low, which is not preferable. The average spacing (Sm) of the unevenness is preferably 4 to 300 nm. Even if it is smaller than 4 nm or larger than 300 nm, the long-term stability of hydrophilic performance is low, which is not preferable. A more preferable range of the average spacing (Sm) of the unevenness is 5 to 150 nm. In this range, the long-term stability of hydrophilic performance is even better. Here, the surface average roughness (Ra) and the average spacing (Sm) of the unevenness are defined by the method described in JIS B 0601 (1994), and an electron microscope (for example, H-600 manufactured by Hitachi, Ltd.) is used. It can be calculated from the observed and measured cross-sectional curves.

[0014] In the present invention, the overcoat layer on the photocatalytic membrane is indispensable for hydrophilicity when not irradiated with light. The overcoat layer is at least one metal oxide selected from silicon oxide, aluminum oxide, titanium oxide, zirconium oxide and cerium oxide (excluding only one type of titanium oxide), and preferably contains 80 wt% or more of silicon oxide. It is a thin film.

[0015] The overcoat layer can be formed by a known method. For example, the sol-gel method (for example, Yuji Yamamoto, Hirokazu Kamiya, Saio Sakuhana, Journal of the Ceramic Society, 90, 328 ~ 333 (1982)), the liquid phase deposition method (for example, Tokuhei 1-59210, Tokuhei 4-13301). ), Vacuum film formation method (vacuum deposition, sputtering), baking method, spray coating (for example, Japanese Patent Application Laid-Open No. 53-124523, Japanese Patent Application Laid-Open No. 56-96749), CVD method (for example, Japanese Patent Application Laid-Open No. 55-90441). , JP-A-1-201046, JP-A-5-208849) and the like are examples.

[0016] The average thickness of the overcoat layer is preferably 0.1 to 50 nm. If the average thickness is less than 0.1 nm, the effect of improving hydrophilicity is not remarkable, and if it is larger than 50 nm, the unevenness of the surface of the titanium oxide layer tends to be filled, and the effect of improving hydrophilicity by ultraviolet irradiation is difficult to be recognized. Not preferable.

[0017] The overcoat layer is preferably a porous material. When the overcoat layer is porous, particularly porous with a pore volume of 1 to 50%, the ability to retain water on the surface is increased, and hydrophilicity is further improved, which is preferable.

[0018] The porous overcoat layer is formed by various methods. For example, it can be formed using the sol-gel method. At least one organic polymer compound selected from the group consisting of polyethylene glycol, polypropylene glycol, and polyvinyl alcohol is added to the coating liquid for forming an overcoat, and the liquid obtained by dissolving these is obtained by forming the photocatalyst. It is obtained by coating and drying on a substrate and further heating at 350 to 650 ° C for 5 minutes to 2 hours to decompose the added organic polymer compound.

[0019] The hydrophilic photocatalyst member according to the present invention can be applied to, for example, mirrors, windowpanes for automobiles, and the like.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Here, FIGS. 1 (a) and 1 (b) are enlarged cross-sectional views of the hydrophilic photocatalyst member according to the present invention, respectively, and FIG. 2 is titanium oxide (TiO).₂It is a figure explaining the crystal plane of).

[0021] In the embodiment shown in (a), the hydrophilic photocatalyst member has titanium oxide (TiO) on the surface of the glass plate 1 as a base material.₂) Layer 2 is formed and this titanium oxide (TiO)₂) Silicon oxide (SiO) as an overcoat layer on the surface of layer 2.₂) It forms a film 3. In the embodiment shown in (b), the glass plate 1 and titanium oxide (TiO) are used.₂) A base film 4 that prevents alkali such as Na from leaching from the glass plate 1 is interposed between the layers 2.

[0022] As the glass plate 1, SiO₂Titanium oxide (TiO) as the main component of soda lime glass₂The layer 2 is formed by a conventionally known method such as a sol-gel method, a liquid phase precipitation method, a vacuum film forming method, a baking method, a spray coating method, a CVD method, or a sputtering method, and has a thickness of 200 nm or more. The surface average roughness (Ra) of the surface is 0.5 to 25 nm. Also, titanium oxide (TiO)₂) Layer 2 has an anatase-type crystal structure.

On the other hand, silicon oxide (SiO)₂) The film 3 is formed by sputtering, and its thickness is 0.1 to 100 nm. And silicon oxide (SiO)₂The film 3 is the titanium oxide (TiO).₂) Titanium oxide (TiO) as it is formed on layer 2.₂) The unevenness of layer 2 is transferred as it is, and silicon oxide (SiO)₂) The surface average roughness (Ra) of the surface of the film 3 is also 0.5 to 25 nm. In addition, it is appropriate that the average spacing (Sm) of the unevenness is in the range of 4 to 300 nm.

[0024] Titanium oxide (TiO₂) Allows the hydrophilic action, antibacterial action and antifouling action of the photocatalyst in the range of crystallite size of 10 nm or more and 50 nm or less. If the crystallite size is smaller than 10 nm, the photocatalytic activity is insufficient. Further, if the crystallite size is larger than 50 nm, the transparency of the thin film is lowered and the film has a high haze rate, which is not preferable.

[0025] Here, anatase-type titanium oxide (TiO)₂) Has its crystal planes (101), (112), (200), (211) and (204) oriented substantially parallel to the substrate surface. Each crystal plane is shown in Fig. 2.

[0026] Fig. 3 shows titanium oxide (TiO).₂) Layer is formed by, for example, DC magnetron sputtering (pressure: 3 mTorr, temperature: 350 ° C), titanium oxide (TiO).₂) X-ray diffraction graph showing the relationship between the layer thickness and the crystal plane, Fig. 4 is the X-ray diffraction graph showing the relationship between the substrate processing temperature and the crystal plane of titanium oxide (thickness: 500 nm), and Fig. 5 is the titanium oxide (thickness: 500 nm). TiO₂) Is an X-ray diffraction graph showing the relationship between the film thickness and the crystal plane when the film formation temperature is changed, and the following (Table 1) to (Table 4) summarize the examples and comparative examples of FIG. It is a thing.

(Example 1) The anti-fog article shown in Example 1 was produced in the following manner.

[Formation of base film] RF magnetron sputtering (target SiO) for the purpose of preventing alkali elution from the glass plate to the titanium oxide film.₂) By₂Was formed. Using a mixed gas of 5 sccm of oxygen gas and 60 sccm of argon gas, under the conditions of gas pressure of 3 mTorr and target input power of 2 kW, SiO is placed on soda lime glass with a thickness of 3 mm and 10 × 10 cm by an in-line RF magnetron sputtering device.₂The undercoat film was formed. Adjust the number of passes for transporting the substrate to a base film (SiO) with a film thickness of 50 nm₂) Was formed. Base film (SiO)₂) Was measured and confirmed using a stylus type profilometer.

[Formation of Titanium Oxide Film] The above SiO₂A titanium oxide layer was formed on the glass plate on which the base film of No. 1 was formed in the following manner. The glass plate is heated to about 350 ° C by the in-line DC magnetron sputtering device (target: Ti) under the conditions of gas (oxygen) 50 sccm, gas pressure 3 mTorr, target input power 3 kW, and the heater in the vacuum device chamber. A film of titanium oxide was formed. A titanium oxide film having a film thickness of 500 nm was formed by adjusting the number of passes for transporting the substrate. Titanium oxide (TiO₂) Was measured and confirmed using a stylus type profilometer.

[Formation of Overcoat Layer] SiO of the overcoat layer is formed on the glass plate on which the above-mentioned base film and titanium oxide film are formed in the following manner.₂A film was formed. An in-line RF magnetron sputtering device (target SiO) using a mixed gas of oxygen gas 5 sccm and argon 60 sccm under the conditions of gas pressure 3 mTorr and target input power 2 kW.₂), The SiO of the overcoat layer on the glass plate on which the base film and titanium oxide film formed above were formed.₂A film was formed. The number of passes for transporting the substrate was adjusted to form an overcoat layer having a film thickness of 10 nm. The film thickness of the overcoat layer was measured and confirmed using a stylus type step meter. As a result, the glass plate / base film (SiO)₂) (50nm) / Titanium oxide layer (TiO₂) (500nm) / Overcoat layer (SiO)₂) (10 nm) was obtained. Let A be the sample obtained in this way.

[Evaluation of photocatalytic activity] Photocatalytic activity was measured by the following triolein decomposition test. Triolein (chemical formula (C)) is placed on the film surface side of the sample cut into 70 mm .₁₇H₃₃COO)₃C₃H₅) Was added dropwise and applied, and the triolein residual rate was compared to evaluate the photocatalytic activity. 3mW / cm on the sample surface by black light from the film surface side to the above sample²It was irradiated with ultraviolet rays of the same intensity for 20 hours. After irradiation with ultraviolet rays, the weight of the sample was measured to determine the residual triolein ratio, which was used as an index of photocatalytic activity. It can be said that the smaller the triolein residual rate, the higher the photocatalytic activity. The triolein residual rate (%) was calculated by the following formula. Triolein residual rate = ((zx) / (yx)) × 100 where x: weight of sample only (g) y: weight of sample coated with triolein before UV irradiation (g) z: after UV irradiation Weight of sample coated with triolein (g) [Measurement of surface roughness and average spacing of irregularities] Arithmetic mean roughness (Ra) (nm) of titanium oxide layer and average spacing of irregularities (Sm) ( nm) was measured by AFM (atomic force microscope).

[Calculation of average crystallite size] The crystallite size of titanium oxide was calculated by the following method. The crystallite size was calculated from Scherrer's formula from the integral width of the peak for each orientation plane obtained by X-ray diffraction measurement. Scherrer's equation ε = λ / (β · cos θ) ε = Crystal size (Å) λ = Measured X-ray wavelength (Å) β = Peak angstrom (radian) θ = Diffraction line Bragg angle (radian) ) [0033] [Evaluation of hydrophilicity] The degree to which the above sample A is left in a room where it is not directly exposed to sunlight but indirectly brightened by sunlight and where people constantly enter and exit, and the surface becomes dirty and the antifogging property deteriorates. Was evaluated by the degree of cloudiness when the exhaled breath was sprayed (expiratory test). That is, the sample immediately after the surface is cleaned does not become cloudy even when exhaled, but the pollutant component in the atmosphere is adsorbed on the sample surface when left indoors and becomes cloudy by the exhalation test. The time from the start of leaving the room to the start of fogging (anti-fog maintenance time) was used as an index of anti-fog maintenance. It can be said that the larger this value is, the higher the anti-fog maintenance property is. The anti-fog retention of these samples was evaluated according to the following (Table 1).

[0034] [Table 1]<img file="JP3904355B2_D0001.tif" />[0035] Furthermore, xenon lamp light (ultraviolet intensity 0.5 mW / cm) was applied to a sample whose antifogging property was reduced by leaving it indoors (fog occurred in the above breath test).²: Measured with UVR-2 / UD-36, an ultraviolet intensity meter manufactured by Topcon Corporation. ) Was continuously irradiated for 30 minutes, and the magnitude of decrease in water droplet contact angle (recovery amount of water droplet contact angle) was used as an index of anti-fog recovery. In addition, 0.5mW / cm²The ultraviolet (340 to 395 nm) irradiation intensity of is equivalent to about 20% of the ultraviolet intensity contained in the direct sunlight from the outdoor sunlight at latitude 35 ° N in winter, fine weather, and noon. If the UV light reduces the water droplet contact angle and restores hydrophilicity, it can be said that the sample has very good anti-fog recovery properties. Using a contact angle meter (CA-DT manufactured by Kyowa Interface Science Co., Ltd.), measure the contact angle for 0.4 mg of water droplets before and after 30 minutes of light irradiation, and how much the contact angle is by ultraviolet irradiation. The water droplet contact angle ratio defined by the value of (contact angle after 30 minutes of light irradiation) / (contact angle before light irradiation) was calculated and evaluated according to the following (Table 2). It can be said that the smaller the water droplet contact angle ratio, the better the anti-fog recovery property by light irradiation.

[0036] [Table 2]<img file="JP3904355B2_D0002.tif" />[0037] Various evaluation results of the above sample A are shown in (Table 3) and (Table 4). It can be seen that sample A is excellent in anti-fog retention and anti-fog recovery.

[0038] [Table 3]<img file="JP3904355B2_D0003.tif" />[0039] [Table 4]<img file="JP3904355B2_D0004.tif" />(Example 2) A glass plate / base film (SiO) in the same manner as in Example 1.₂) (50nm) / Titanium oxide layer (TiO₂) (1000nm) / Overcoat layer (SiO)₂) (10 nm) was formed. Let B be the sample obtained in this way. The results of various anti-fog property evaluations of Sample B are shown in (Table 3) and (Table 4).

(Comparative Example 1) Glass plate / base film (SiO)₂) (50nm) / Titanium oxide layer (TiO₂) (500 nm) was formed. When the titanium oxide layer was formed, the substrate was not heated and the film was formed at room temperature. Let C be the sample obtained in this way. The results of various anti-fog property evaluations of Sample C are shown in (Table 3) and (Table 4).

(Comparative Example 2) Glass plate / base film (SiO)₂) (50nm) / Titanium oxide layer (TiO₂) (200 nm) was formed. Let D be the sample obtained in this way. The results of various anti-fog property evaluations of Sample D are shown in (Table 3) and (Table 4).

(Comparative Example 3) In the same manner as in Comparative Example 2, the glass plate / base film (SiO).₂) (50nm) / Titanium oxide layer (TiO₂) (50 nm) was formed. Let E be the sample obtained in this way. The results of various anti-fog property evaluations of Sample E are shown in (Table 3) and (Table 4).

(Comparative Example 4) Glass plate / base film (SiO)₂) (50nm) / Titanium oxide layer (TiO₂) (1000 nm) was formed. When the titanium oxide layer was formed, the substrate was not heated and the film was formed at room temperature. Let F be the sample obtained in this way. The results of various anti-fog property evaluations of Sample F are shown in (Table 3) and (Table 4).

(Comparative Example 5) A glass plate / base film (SiO) in the same manner as in Example 1 except that an overcoat layer is not formed.₂) (50nm) / Titanium oxide layer (TiO₂) (500 nm) was formed. Let G be the sample obtained in this way. The results of various anti-fog property evaluations of Sample G are shown in (Table 3) and (Table 4).

[Comparative Example 6] A glass plate / base film (SiO) in the same manner as in Example 2 except that an overcoat layer is not formed.₂) (50nm) / Titanium oxide layer (TiO₂) (1000 nm) was formed. Let H be the sample obtained in this way. The results of various antifogging property evaluations of Sample H are shown in (Table 3) and (Table 4).

(Comparative Example 7) A glass plate / base film (SiO) in the same manner as in Example 1.₂) (50nm) / Titanium oxide layer (TiO₂) (500nm) / Overcoat layer (SiO)₂) (10 nm) was formed. When the titanium oxide layer was formed, the substrate was not heated and the film was formed at room temperature. Let J be the sample obtained in this way. The results of various anti-fog property evaluations of Sample J are shown in (Table 3) and (Table 4).

[0048] From the above figures and (Table), in order to fully exert the effect of the photocatalyst, at least the crystal planes (101), (112) and (211) are oriented substantially parallel to the surface of the substrate. It is required to be, for this purpose titanium oxide (TiO₂It can be seen that the thickness of the layer) needs to be more than 200 nm, more preferably 500 nm or more, and the substrate temperature (deposition temperature) needs to be about 230 ° C or more.

[Effect of the Invention] As described above, the hydrophilic photocatalyst member according to claim 1 is a member.<u style="single">A titanium oxide layer as a catalyst is formed with a thickness of 500 nm or more on the surface of the substrate heated to 230 ° C or higher by the DC magnetron sputtering method, either directly or through a base film for blocking alkali.</u>An overcoat layer is formed on the surface of the titanium oxide layer, the titanium oxide layer has an anatase-type crystal structure, and the crystal planes (101), (112) and (211) are substantially parallel to the surface of the substrate. In the hydrophilic photocatalyst member according to claim 1 or 2, the crystal face size of the titanium oxide layer is 10 nm or more and 50 nm or less in the hydrophilic photocatalyst member according to claim 3. , Not only hydrophilic action, but also photocatalytic action such as antibacterial action and antifouling action is fully exhibited.

BRIEF DESCRIPTION OF THE DRAWINGS [Fig. 1] (a) and (b) are enlarged cross-sectional views of a hydrophilic photocatalyst member according to the present invention, respectively. [Fig. 2] Titanium oxide (TiO).₂(Fig. 3) Titanium oxide (TiO)₂) X-ray diffraction graph showing the relationship between the layer thickness and the crystal plane [Fig. 4] X-ray diffraction graph showing the relationship between the substrate processing temperature and the crystal plane [Fig. 5] Crystal plane by changing the film thickness and the crystal plane X-ray diffraction graph showing the relationship with [Explanation of symbols] 1 ... glass plate, 2 ... titanium oxide (TiO₂) Layer, 3 ... Silicon Oxide (SiO)₂) Membrane, 4 ... Underground film.